throat/leade angle.

[bruce moulds]

while this did not happen with an fclass rifle, it still raises a question.
loads were worked up for a 9.3X64 brenneke lothar walther barrel that were quite safe, and had good speed.
had it throated longer to seat bullets out further, and safe loads blew primers.
one would have expected lower pressures!
study of chamber drawings for this cartridge showed a very low throat leade angle compared to 1deg30min common today.
a ptg throater altered the angle back to correct, and all is back to normal.
the ammount of pressure change was quite a surprise.
where this relates to fclass is the question of attainabble speed from a given barrel.
weatherby always claimed more speed from long freebore, but this might not be suitable for extreme accuracy, and urban myth states that it just needs more powder for the same speed.
lower leade throat angles (like 1/2 degree) might well offer more potential speed for same pressure with good accuracy as well.
urban myth might have to be overcome on this, but it is a good question.
keep safe,
bruce.

[AlanF]

"...had it throated longer to seat bullets out further, and safe loads blew primers..."

Bruce,

Can you clarify this please? Does "safe loads" mean same velocity, or same powder charge, and if same powder charge, what was the velocity change?

[bruce moulds]

sorry alan.
safe loads refers to good safe loads in the original throat.
same ammo, same coal, (more jump) fired in the rethroated chamber blew primers.
the rethroated chamber allowed a longer cartridge oal, so one would have expacted reduced pressure.
when recthroated a second time with a lower angle, pressures dropped again.
keep safe,
bruce.